Step 1: Preheat oven to 400°F (200°C).
Step 2: In a large roasting pan or on a baking sheet, combine the halved/quartered tomatoes and unpeeled garlic cloves. Drizzle generously with 1/4 cup olive oil. Season with 1 teaspoon salt, 1/2 teaspoon black pepper, and red pepper flakes (if using). Toss until everything is well coated.
Step 3: Roast for 30-40 minutes, or until the tomatoes are blistered and slightly charred, and the garlic cloves are very soft. Gently shake the pan halfway through for even roasting.
Step 4: While tomatoes are roasting, cook pasta according to package directions in a large pot of salted boiling water until al dente. Reserve 1 cup of the starchy pasta water before draining the pasta.
Step 5: Once roasted, remove the pan from the oven. Let the garlic cool for a few minutes, then squeeze the soft, roasted garlic pulp out of its skins directly into the pan with the tomatoes. Discard the skins.
Step 6: Using a fork or potato masher, gently mash some of the roasted tomatoes and garlic in the pan to create a rustic sauce. Leave some chunks for texture.
Step 7: Add the drained pasta directly to the roasting pan. Add about 1/2 cup of the reserved pasta water and toss vigorously to combine, allowing the sauce to emulsify and coat the pasta. Add more pasta water, 1 tablespoon at a time, if a thinner sauce is desired.
Step 8: Stir in the fresh basil leaves, Parmesan cheese (if using), and a final drizzle of good quality extra virgin olive oil. Taste and adjust seasoning with more salt and pepper as needed. Serve immediately, garnished with extra fresh basil and Parmesan if desired.